Resin composition for primer

ABSTRACT

The present invention provides a resin composition for a primer comprising (a) 100 parts by weight of a chlorinated polyolefin having a chlorine content of 5-50 wt. % and a weight-average molecular weight of 30000-120000, and (b) 15-80 parts by weight of a hydroxyl-containing petroleum resin.

TECHNICAL FIELD

[0001] The present invention relates to a resin composition for a primerthat has excellent adhesion to substrates of polypropylene and likepolyolefin resins and to melamine and various like coatings and hasexcellent low-temperature storage stability.

BACKGROUND OF THE INVENTION

[0002] Offering many advantages such as high productivity, high designflexibility, light weight, rustproofing, high impact resistance, etc.,plastics are used these days in a wide variety of applications forautomotive parts, electronic parts, building materials and the like. Inparticular, since polyolefin resins are inexpensive and have excellentmoldability, chemical resistance, water resistance, impact resistance,and electrical properties, they have been widely used as industrialmaterials and are one of the types of material for which demand isexpected to further increase in the future.

[0003] However, unlike acrylic resins and similar synthetic polarresins, polyolefin resins have drawbacks due to their crystallinity andnonpolarity, i.e., it is difficult to coat or bond them. Primerscontaining weakly chlorinated polyolefins that are chlorinated to 10-40wt. % as a binder have heretofore been used to coat or bond suchlow-adhesion polyolefin resins.

[0004] When the cost of transportation or the amount of solvent used isconsidered, primers should preferably have a large solids content.However, an excessive solids content results in decreased flowability orincreased viscosity at low temperatures, adversely affecting primers inpractical applications, for example, impaired solubility in coatings andworkability during spray coating. Moreover, the storage stability at lowtemperatures is also adversely affected. To control viscosity, if themolecular weight of the resins is lowered by degradation or likemethods, or low-molecular-weight rosin ester resins are added, theinitial adhesion and gasohol resistance are significantly impaired.

[0005] Recently, the coating technique typically employed to reducecoating lines or costs is wet-on-wet coating in which primers andcoatings are applied sequentially and baked only once. However, withsuch coating methods, it has been impossible to obtain sufficientadhesion particularly when melamine coatings are used. This ispresumably because intermediate layers are created between primers andmelamine coatings due to the high polarity of melamine resins and thelow polarity of conventional primers. Therefore.,resin compositions forhigh polarity primers are required.

DISCLOSURE OF THE INVENTION

[0006] An object of the present invention is to provide a resincomposition for a primer that has excellent adhesion to polyolefin resinsubstrates and melamine coatings and has enhanced low-temperaturestorage stability and gasohol resistance.

[0007] Other objects and characteristics of the present invention willbecome evident by the disclosure provided hereinbelow.

[0008] The inventors conducted extensive research and found that thecombination of a specific chlorinated polyolefin and a specifichydroxyl-containing petroleum resin can attain the objects describedabove. The inventors thereby accomplished the present invention.

[0009] In particular, the present invention provides the resincompositions for primers described below:

[0010] Item 1. A resin composition for a primer comprising (a) 100 partsby weight of a chlorinated polyolefin having a chlorine content of 5-50wt. % and a weight-average molecular weight of 30000-120000, and (b)15-80 parts by weight of a hydroxyl-containing petroleum resin.

[0011] Item 2. The resin composition for a primer according to Item 1further comprising (c) an organic solvent.

[0012] Item 3. The resin composition for a primer according to Item 1 or2, wherein the chlorinated polyolefin is an acid-modified chlorinatedpolyolefin produced by graft-copolymerization with 1-10 wt. % of atleast one member selected from the group consisting of α, β-unsaturatedcarboxylic acids and their acid anhydrides.

[0013] Item 4. The resin composition for a primer according to any oneof Items 1-3, wherein the hydroxyl-containing petroleum resin has ahydroxyl value of 10-250 mgKOH/g.

[0014] Item 5. The resin composition for a primer according to any oneof Items 1-4, wherein the hydroxyl-containing petroleum resin has asoftening point of 60-200° C. and a weight-average molecular weight of200-3000.

[0015] Item 6. The resin composition for a primer according to any oneof Items 1-5, wherein the hydroxyl-containing petroleum resin ishydrogenated.

[0016] Item 7. The resin composition for a primer according to any oneof Items 2-6, wherein the organic solvent is at least one memberselected from the group consisting of aromatic hydrocarbons, alicyclichydrocarbons, esters and ketones.

[0017] Chlorinated polyolefins usable herein may be produced bychlorinating polyolefins. Examples thereof include those that arefurther acid-modified and contain carboxyl group(s). Such chlorinatedpolyolefins can be readily produced according to known methods. Forexample, acid-modified chlorinated polyolefins can be obtained bygraft-copolymerizing starting polyolefins with at least one memberselected from the group consisting of α, β-unsaturated carboxylic acidsand their acid anhydrides, and then injecting chlorine gas in thepresence of a solvent. They can also be obtained by chlorinatingstarting polyolefins and then graft-copolymerizing the chlorinatedpolyolefins with at least one member selected from the group consistingof α, β-unsaturated carboxylic acids and their acid anhydrides.

[0018] Examples of starting polyolefins are propylene-based polyolefinsincluding crystalline polypropylenes, noncrystalline polypropylenes andpropylene-ethylene copolymers. Such polymers can be used alone or incombination. Among these, preferable are crystalline polypropylenes suchas isotactic polypropylene and syndiotactic polypropylene, withisotactic polypropylene being particularly preferable.

[0019] Examples of α, β-unsaturated carboxylic acids and their acidanhydrides to be graft-copolymerized with starting polyolefins orchlorinated polyolefins are maleic acid, maleic anhydride, itaconicacid, itaconic anhydride, fumaric acid, etc. Among these, preferable areacid anhydrides, with maleic anhydride being particularly preferable.The amount to be graft-copolymerized is preferably 1-10 wt. % and morepreferably 1-6 wt. %.

[0020] To graft copolymerize, starting polyolefins or chlorinatedpolyolefins are dissolved in an aromatic organic solvent such astoluene, xylene or the like, or thermally fused without a solvent; andreacted with at least one member selected from the group consisting ofα, β-unsaturated carboxylic acids and their acid anhydrides in thepresence of a radical generator.

[0021] Examples of radical generators usable in the graftcopolymerization include peroxides such as di-tert-butyl peroxide,tert-butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, methylethyl ketone peroxide, etc.

[0022] To obtain chlorinated polyolefins by chlorination, startingpolyolefins or acid-modified polyolefins are dispersed or dissolved in achlorinated solvent such as chloroform, carbon tetrachloride,tetrachloroethylene or the like, and reacted in the presence of acatalyst by injecting chlorine gas under ambient or increased pressureat 80-120° C.

[0023] The chlorine content of the chlorinated polyolefins (includingthe acid-modified chlorinated polyolefins) is 5-50 wt. %, preferably10-40 wt. %.

[0024] The weight-average molecular weight of the chlorinatedpolyolefins (including the acid-modified chlorinated polyolefins) is30000-120000, preferably 40000-80000.

[0025] Hydroxyl-containing petroleum resins usable herein refer topetroleum resins containing hydroxyl group(s) in their molecularstructure due to some chemical bonding. Methods for producing suchhydroxyl-containing petroleum resins are not limited. In view ofindustrial convenience, such petroleum resins are usually those that canbe obtained by reacting polymerizable monomers contained in petroleumfractions with hydroxyl-containing compounds.

[0026] Examples of polymerizable monomers contained in petroleumfractions are isoprene, n-pentene, methylbutene, pentadiene,cyclopentene and like monomers of the C5 fraction; styrene,vinyltoluene, α-methylstyrene, indene, methyl indene and like monomersof the C9 fraction; cyclopentadiene, methylcyclopentadiene,ethylcyclopentadiene and like monomers of the cyclopentadiene portionincluding the dimers, trimers and codimers thereof; etc.

[0027] Hydroxyl-containing compounds refer to phenolic compounds andhydroxyl-containing olefins. Examples thereof include phenols; cresol,xylenol, p-tert-butylphenol, p-octylphenol, nonylphenol, vinylphenol andlike alkyl-substituted phenols; allyl alcohol, crotyl alcohol,1,4-butenediol, hydroxyethyl acrylate, hydroxyethyl methacrylate;3-methyl-2-propene-1-ol, 2-methyl-2-propene-1-ol and likealkyl-substituted allyl alcohols; etc.

[0028] Methods for producing the hydroxyl-containing petroleum resinsare not limited, and known methods can be employed. Examples include amethod wherein a polymerizable monomer and a hydroxyl-containingcompound are polymerized in the presence of a Friedel-Crafts catalyst; amethod wherein a polymerizable monomer and a hydroxyl-containingcompound are polymerized in the presence of a radical polymerizationinitiator; a method wherein a polymerizable monomer and ahydroxyl-containing compound are thermally polymerized in an autoclave;and like methods.

[0029] Specific examples of the hydroxyl-containing petroleum resins arealcohol-modified dicyclopentadiene resins, alcohol-modifiedC9-dicyclopentadiene resins, phenol-modified C9-dicyclopentadieneresins, phenol-modified dicyclopentadiene resins, phenol-modified C9petroleum resins, etc.

[0030] The olefin portion of the hydroxyl-containing petroleum resinsmay be stabilized as necessary by hydrogenation, hydration, oxidation,hydroboration, hydrohalogenation, halogenation, etc. Among thesemethods, hydrogenation is preferable since it is industrially convenientand can improve the color, odor and stability of the resin.Hydrogenation can be carried out according to conventional methods.

[0031] Although the extent of hydrogenation of the aromatic portion orolefinic portion of the hydroxyl-containing hydrogenated petroleumresins is not limited, it is preferable to completely hydrogenate theolefinic portion to improve color and stability.

[0032] Alternatively, the stability and color of the hydroxyl-containingpetroleum resins may be improved by adding antioxidants, UV absorbers,reducing agents, etc.

[0033] The softening point of the hydroxyl-containing petroleum resinsusable herein is preferably 60-200° C. Although it depends on theapplication, the softening point is preferably 70° C. or greater,particularly preferably 80-130° C., since excessively low softeningpoints result in decreased heat resistance.

[0034] The weight-average molecular weight of the hydroxyl-containingpetroleum resins is preferably 200-3000, more preferably 200-2000.

[0035] The hydroxyl value of the hydroxyl-containing petroleum resins ispreferably 10-250 mgKOH/g, more preferably 20-220 mgKOH/g.

[0036] In the present invention, the ratio of (b) thehydroxyl-containing petroleum resin to (a) the chlorinated polyolefin is15-80 parts by weight, preferably 20-75 parts by weight, ofhydroxyl-containing petroleum resin relative to 100 parts by weight ofchlorinated polyolefin. When the hydroxyl-containing petroleum resin isused in less than 15 parts by weight, the effect of using thehydroxyl-containing petroleum resin is barely obtained. When it is usedin more than 80 parts by weight, the adhesion and gasohol resistance ofthe resulting resin composition for a primer tend to be impaired.

[0037] The resin composition for a primer of the present invention isusually dissolved in (c) an organic solvent for use. Examples of usableorganic solvents are toluene, xylene and like aromatic hydrocarbons;cyclohexane, methylcyclohexane, ethylcyclohexane and like alicyclichydrocarbons; ethyl acetate, butyl acetate and like esters; and methylethyl ketone, methyl isobutyl ketone and like ketones. These solventsmay be used alone or in combination. The amount of organic solvent to beused is preferably 100-10000 parts by weight, more preferably 100-1000parts by weight, per 100 parts by weight of chlorinated polyolefin.

[0038] The resin composition for a primer of the present invention canbe obtained either by mixing an organic solvent solution of (a) thechlorinated polyolefin with an organic solvent solution of (b) thehydroxyl-containing petroleum resin, or by kneading (a) the chlorinatedpolyolefin and (b) the hydroxyl-containing petroleum resin by anextruder to pelletize and dissolving the pellets in an organic solvent.

[0039] Stabilizers, thickeners, surfactants, etc., can be added asnecessary to the resin composition for a primer of the present inventioninsofar as its properties are not impaired.

[0040] The resin composition for a primer of the present inventionexhibits excellent adhesion to polyolefin resin substrates and variouscoatings such as melamine coatings and has enhanced low-temperaturestorage stability and gasohol resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] Examples are given below to illustrate the invention in moredetail, but the scope of the invention is not limited to these examples.

PRODUCTION EXAMPLE 1 Maleic Anhydride-Modified Chlorinated Polypropylene

[0042] Isotactic polypropylene (weight-average molecular weight: 50000,275 parts by weight), 19.3 parts by weight of maleic anhydride, 5.5parts by weight of dicumyl peroxide, and 412.5 parts by weight oftoluene were introduced into an autoclave equipped with an stirrer, and,after 5 minutes of nitrogen charging, reacted while stirring for 5 hoursat 140° C. After this reaction, the reaction solution was introducedinto an excess of methyl ethyl ketone to precipitate a resin. This resinwas further washed with methyl ethyl ketone several times to removeunreacted maleic anhydride, thereby giving maleic anhydride-modifiedpolypropylene.

[0043] Two hundred parts by weight of this maleic anhydride-modifiedpolypropylene and 1800 parts by weight of tetrachloroethylene wereintroduced into a four-neck flask and, after 5 minutes of nitrogencharging, stirred while heating to 110° C. to dissolve the resin. Twoparts by weight of di-tert-butyl peroxide was added, and chlorine gaswas introduced. After chlorine gas (140 parts by weight) was introducedfor 3 hours, nitrogen gas was introduced to remove hydrogen chloride andunreacted chlorine gas. The solvent, i.e., tetrachloroethylene, wasdistilled under reduced pressure by an evaporator, and then toluene wasadded in replacement, thereby giving a solution of maleicanhydride-modified chlorinated polypropylene (hereinafter referred to as“Chlorinated Polyolefin A”, weight-average molecular weight: 40000,chlorine content: 21 wt. %, amount of graft-copolymerized maleicanhydride: 1.7 wt. %) in toluene.

PRODUCTION EXAMPLE 2 Phenol-Modified C9 Petroleum Resin

[0044] A cracked distillate fraction with a boiling range of 140-280° C.generated during the steam-cracking of naphtha was used as 100 parts byweight of starting oil. Using 0.6 wt. % of boron trifluoride phenolaterelative to the starting oil, polymerization was carried out for 3 hoursat 30° C. in the presence of 3 parts by weight of phenol. Calciumhydroxide (3 parts by weight) was added to the polymerized oil thusobtained, and the mixture was stirred for 1 hour at 70° C. toneutralize, and 3 parts by weight of activated clay was further addedand the mixture was stirred for 30 more minutes. The polymerized oilobtained by filtering off the calcium hydroxide and activated clay wasdistilled at 200° C. at 2.7 kPa for 15 minutes, thereby givingHydroxyl-Containing Petroleum Resin A having a softening point of 105°C., a color of 9 Gardner, a hydroxyl value of 72 mgKOH/g, and aweight-average molecular weight of 1350 (polystyrene equivalent obtainedby gel permeation chromatography (GPC)).

PRODUCTION EXAMPLE 3 Phenol-Modified Dicyclopentadiene Resin

[0045] Dicyclopentadiene (100 parts by weight), 100 parts by weight ofphenol and 80 parts by weight of xylene were introduced into anautoclave and reacted for 4 hours at 260° C. in a nitrogen atmosphere,thereby giving a polymerized oil. This polymerized oil was distilled at200° C. at 2.7 kPa for 15 minutes to remove unreacted monomers,oligomers and the solvent, thereby giving Hydroxyl-Containing PetroleumResin B having a softening point of 111° C., a color of 10 Gardner, ahydroxyl value of 157 mgKOH/g, and a weight-average molecular weight of580 (polystyrene equivalent obtained by GPC).

PRODUCTION EXAMPLE 4 Alcohol-Modified Dicyclopentadiene Resin

[0046] Dicyclopentadiene (100 parts by weight), 100 parts by weight ofallyl alcohol and 80 parts by weight of xylene were introduced into anautoclave and reacted for 2 hours at 270° C. in a nitrogen atmosphere,thereby giving a polymerized oil. This polymerized oil was distilled toremove unreacted monomers, oligomers and the solvent at 200° C. at 2.7kPa for 15 minutes, thereby giving Hydroxyl-Containing Petroleum Resin Chaving a softening point of 97.5° C., a color of 8 Gardner, a hydroxylvalue of 210 mgKOH/g, and a weight-average molecular weight of 540(polystyrene equivalent obtained by GPC).

PRODUCTION EXAMPLE 5 Hydrogenated Alcohol-Modified DicyclopentadieneResin

[0047] Hydroxyl-Containing Petroleum Resin C as obtained in ProductionExample 4 (100 parts by weight), 100 parts by weight of cyclohexane and0.4 parts by weight of a stabilized nickel catalyst (manufactured byNikki Chemical CQ., Ltd., trade name: “N-113”) were introduced into anautoclave and reacted for 5 hours at 270° C. in a pressurized hydrogenatmosphere at 18 MPa. After filtering off the catalyst, the reactionmixture was distilled at 200° C. at 2.7 kPa for 15 minutes, therebygiving Hydroxyl-Containing Petroleum Resin D having a softening point of93° C., a color of 1 Gardner or less (200 Hazen), a hydroxyl value of143 mgKOH/g, and a weight-average molecular weight of 530 (polystyreneequivalent obtained by GPC).

PRODUCTION EXAMPLE 6 Hydrogenated Alcohol-Modified DicyclopentadieneResin

[0048] Hydroxyl-Containing Petroleum Resin C as obtained in ProductionExample 4 (100 parts by weight), 100 parts by weight of cyclohexane and2.0 parts by weight of a stabilized nickel catalyst (manufactured byNikki Chemical Co., Ltd., trade name: “N-113”) were introduced into anautoclave and reacted for 5 hours at 240° C. in a pressurized hydrogenatmosphere at 18 MPa. After filtering off the catalyst, the reactionmixture was distilled at 220° C. at 0.27 kPa for 30 minutes, therebygiving Hydroxyl-Containing Petroleum Resin E having a softening point of118° C., a color of 1 Gardner or less (300 Hazen), a hydroxyl value of190 mgKOH/g, and a weight-average molecular weight of 600 (polystyreneequivalent obtained by GPC).

EXAMPLE 1

[0049] Chlorinated Polyolefin A was used as the chlorinated polyolefinand Hydroxyl-Containing Petroleum Resin A was used as thehydroxyl-containing petroleum resin. Twenty-wt. % toluene solutions wereprepared for the chlorinated polyolefin and the hydroxyl-containingpetroleum resin respectively. Both toluene solutions were mixed usingthe formulation (parts by weight) shown in Table 1 and sufficientlystirred, thereby giving a resin composition for a primer.

[0050] This resin composition for a primer was sprayed in an amount toattain a solid content of 6 g/m² onto a polypropylene substrate(manufactured by Mitsui Toatsu Chemicals, Inc.) degreased by isopropylalcohol and left to stand for 10 minutes at room temperature to dry. Atwo-component urethane coating (manufactured by Kansai Paint Co., Ltd.,“Retan PG80”) was further spray-coated thereon in an amount of 60 g/m²,and the substrate was dried for 30 minutes at 80° C. Similarly, apolypropylene substrate coated with the aforementioned resin compositionfor a primer was coated with a one-component melamine coating(manufactured by Kansai Paint Co., Ltd.) in the same manner as above,and the substrate was dried for 30 minutes at 120° C.

[0051] The low-temperature storage stability of the aforementioned resincomposition for a primer and the properties of the coated films wereevaluated according to the following methods. Table 2 shows the results.

[0052] [Low-Temperature Storage Stability]

[0053] The resin composition for a primer was left to stand at −5° C.for up to 30 days. During that period, the number of days was counteduntil the resin composition started to gelate.

[0054] [Initial Adhesion (Bonding)]

[0055] Four days after drying, the coated surfaces of the test pieceswere provided with a grid pattern of a hundred 1-mm squares by a cutterthat reached through to the underlying polypropylene substrate. Anadhesive cellophane tape was securely placed on the coated surfaces, andthe tape was quickly peeled horizontal to the surface. This procedurewas repeated 10 times. The test pieces were graded according to how manytimes the tape peeling was conducted before a square created on thecoated surfaces was removed, i.e., if square(s) were removed the firsttime the tape peeling was conducted, this test piece was given 0 points,and if square(s) were removed the second time the tape peeling wasconducted, this test piece was given 1 point. If a test piece exhibitedno removal after ten rounds of tape peeling, this test piece was given10 points, with 10 being full marks.

[0056] [Gasohol Resistance]

[0057] Seven days after drying, coated test pieces whose two ends hadbeen cut off were immersed in a gasoline mixture (conventional unleadedgasoline:ethanol=9:1). The time taken for the coating to peel to adistance of 3 mm from a cut edge of the coated test pieces was measured.

[0058] [Moisture Resistance]

[0059] Coated test pieces were immersed in 40° C. warm water for 240hours. The condition of the coated surface was visually observed andevaluated. The evaluation scale consists of A: excellent, B: good, andC: poor.

EXAMPLES 2-5

[0060] As shown in Table 1, resin compositions for a primer wereprepared in the same manner as in Example 1 except thatHydroxyl-Containing Petroleum Resin A was replaced withHydroxyl-Containing Petroleum Resin B, C, D or E. These resincompositions were evaluated and the results are shown in Table 2.

EXAMPLE 6

[0061] As shown in Table 1, a resin composition for a primer wasprepared in the same manner as in Example 4 except that the amount ofthe toluene solution of Hydroxyl-Containing Petroleum Resin D wasaltered to 25 parts by weight. This resin composition was evaluated andthe results are shown in Table 2.

EXAMPLE 7

[0062] As shown in Table 1, a resin composition for a primer wasprepared in the same manner as in Example 4 except that the amount ofthe toluene solution of Hydroxyl-Containing Petroleum Resin D wasaltered to 66 parts by weight. This resin composition was evaluated andthe results are shown in Table 2.

COMPARATIVE EXAMPLE 1

[0063] A toluene solution of Chlorinated Polyolefin A, which does notcontain a hydroxyl-containing petroleum resin, was used as a resincomposition for a primer, and the properties thereof were evaluated.Table 2 shows the results.

COMPARATIVE EXAMPLE 2

[0064] As shown in Table 1, a resin composition for a primer wasprepared in the same manner as in Example 1 except thatHydroxyl-Containing Petroleum Resin A was replaced with a glycerol esterof rosin (weight-average molecular weight: 920, softening point: 100°C.). This resin composition was evaluated and the results are shown inTable 2.

COMPARATIVE EXAMPLE 3

[0065] As shown in Table 1, a resin composition for a primer wasprepared in the same manner as in Example 1 except thatHydroxyl-Containing Petroleum Resin A was replaced with an unmodified C9petroleum resin that contained no hydroxyl groups (weight-averagemolecular weight: 1100, softening point: 100° C.). This resincomposition was evaluated and the results are shown in Table 2. TABLE 1Comp. Comp. Comp. Resin Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 1Ex. 2 Ex. 3 Chlorinated Polyolefin A 100 100 100 100 100 100 100 100 100100 Hydroxyl-Containing  43 — — — — — — — — — Petroleum Resin AHydroxyl-Containing —  43 — — — — — — — — Petroleum Resin BHydroxyl-Containing — —  43 — — — — — — — Petroleum Resin CHydroxyl-Containing — — —  43 —  25  66 — — — Petroleum Resin DHydroxyl-Containing — — — —  43 — — — — — Petroleum Resin E GlycerolEster of Rosin — — — — — — — —  43 — Unmodified C9 Petroleum — — — — — —— — —  43 Resin

[0066] TABLE 2 Low-Temperature Adhesion (Points) Gasohol ResistanceMoisture Resistance Storage Stability Urethane Melamine UrethaneMelamine Urethane Melamine Ex. 1 Flowable after 30 10 10 No Peelingafter 2- No Peeling after 2- A A Days Hour Immersion Hour Immersion Ex.2 Flowable after 30 10 10 No Peeling after 2- No Peeling after 2- A ADays Hour Immersion Hour Immersion Ex. 3 Flowable after 30 10 10 NoPeeling after 2- No Peeling after 2- A A Days Hour Immersion HourImmersion Ex. 4 Flowable after 30 10 10 No Peeling after 2- No Peelingafter 2- A A Days Hour Immersion Hour Immersion Ex. 5 Flowable after 3010 10 No Peeling after 2- No Peeling after 2- A A Days Hour ImmersionHour Immersion Ex. 6 Flowable after 30 10 10 No Peeling after 2- NoPeeling after 2- A A Days Hour Immersion Hour Immersion Ex. 7 Flowableafter 30 10 10 No Peeling after 2- No Peeling after 2- A A Days HourImmersion Hour Immersion Comp. Not Flowable after 1 10 10 No Peelingafter 2- Peeling after 1- A A Ex. 1 Day Hour Immersion Hour ImmersionComp. Flowable after 30 6 6 Peeling after 1- Peeling after 30- A A Ex. 2Days Hour Immersion Minute Immersion Comp. Flowable after 30 5 5 Peelingafter 1- Peeling after 30- A A Ex. 3 Days Hour Immersion MinuteImmersion

[0067] As is clear from Table 2, compared with the resin composition fora primer of Comparative Example 1, the resin compositions for a primerof Examples 1-7 exhibit increased low-temperature storage stability and,with respect to the melamine coating, enhanced gasohol resistance.Furthermore, compared with the resin compositions for a primer ofComparative Examples 2 and 3, the resin compositions for a primer ofExamples 1-7 exhibit increased adhesion and gasohol resistance.

1. A resin composition for a primer comprising (a) 100 parts by weightof a chlorinated polyolefin having a chlorine content of 5-50 wt. % anda weight-average molecular weight of 30000-120000, and (b) 15-80 partsby weight of a hydroxyl-containing petroleum resin.
 2. The resincomposition for a primer according to claim 1 further comprising (c) anorganic solvent.
 3. The resin composition for a primer according toclaim 1, wherein the chlorinated polyolefin is an acid-modifiedchlorinated polyolefin produced by graft-copolymerization with 1-10 wt.% of at least one member selected from the group consisting of α,β-unsaturated carboxylic acids and their acid anhydrides.
 4. The resincomposition for a primer according to claim 1, wherein thehydroxyl-containing petroleum resin has a hydroxyl value of 10-250mgKOH/g.
 5. The resin composition for a primer according to claim 1,wherein the hydroxyl-containing petroleum resin has a softening point of60-200° C. and a weight-average molecular weight of 200-3000.
 6. Theresin composition for a primer according to claim 1, wherein thehydroxyl-containing petroleum resin is hydrogenated.
 7. The resincomposition for a primer according to claim 2, wherein the organicsolvent is at least one member selected from the group consisting ofaromatic hydrocarbons, alicyclic hydrocarbons, esters and ketones. 8.The resin composition for a primer according to claim 2, wherein thechlorinated polyolefin is an acid-modified chlorinated polyolefinproduced by graft-copolymerization with 1-10 wt. % of at least onemember selected from the group consisting of α, β-unsaturated carboxylicacids and their acid anhydrides.